Generally, class-AB drivers are used to deliver power to small resistors, such as audio amplifiers and/or large capacitors, such as power amplifiers. Typically, these class-AB drivers are required to have rail-to-rail output swing, low quiescent power, large driver capability, high speed and low distortion, etc. However, tradeoffs between these requirements are to be made to get a desired performance. For example, for a given capacitive load, to get sufficient speed, the trans-conductance (gm) has to be increased as the pole is generally in the form of gm/C. Depending on the application, other additional requirements may be added. For wideband applications, such as the one using the whole High Frequency (HF)/Very High Frequency (VHF) Industrial, Scientific and Medical (ISM) band, the additional requirements can be the low in-band attenuation and the high out-band attenuation.
For example, a typical class-AB driver used to deliver power to the small resistors and/or large capacitors may include a push pull output stage, a trans-linear loop, an input stage, a current biasing and enabling circuit, and a VGS (Voltage difference between Gate and Source) multiplier circuit. In typical class AB drivers, the trans-linear loop formed by complementary transistors of CMOS type or Bipolar type, etc. are used for easy biasing implementation and improved linearity by reducing crossover distortion. However, the trans-linear loop of the class AB drivers generates a left-half-plane (LHP) zero due to the imbalance between two signals traveling paths. One signal traveling path (e.g., upper path) starts from input terminal node of the class-AB driver to input node of the trans-linear loop (e.g., say node A) and arrives at an output terminal node via a node (e.g., say node B). The other signal traveling path (e.g., lower path) starts from input terminal node to the node A and arrives at the output terminal node via another node (e.g., say node C). However, the two signal traveling paths may have different speeds with one being faster than the other. Thus, when the two signals coming via the two signal traveling paths are combined, a close-in LHP zero is formed which may significantly reduce the class-AB driver's frequency response performance.